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/*
* Copyright (C) 2011, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef DenormalDisabler_h
#define DenormalDisabler_h
#include <cmath>
#include <cinttypes>
#include <cstring>
#include <float.h>
namespace WebCore {
// Deal with denormals. They can very seriously impact performance on x86.
// Define HAVE_DENORMAL if we support flushing denormals to zero.
#if defined(XP_WIN) && defined(_MSC_VER)
// Windows compiled using MSVC with SSE2
# define HAVE_DENORMAL 1
#endif
#if defined(__GNUC__) && defined(__SSE__)
# define HAVE_DENORMAL 1
#endif
#if defined(__arm__) || defined(__aarch64__)
# define HAVE_DENORMAL 1
#endif
#ifdef HAVE_DENORMAL
class DenormalDisabler {
public:
DenormalDisabler() : m_savedCSR(0) { disableDenormals(); }
~DenormalDisabler() { restoreState(); }
// This is a nop if we can flush denormals to zero in hardware.
static inline float flushDenormalFloatToZero(float f) { return f; }
private:
unsigned m_savedCSR;
# if defined(__GNUC__) && defined(__SSE__)
static inline bool isDAZSupported() {
# if defined(__x86_64__)
return true;
# else
static bool s_isInited = false;
static bool s_isSupported = false;
if (s_isInited) {
return s_isSupported;
}
struct fxsaveResult {
uint8_t before[28];
uint32_t CSRMask;
uint8_t after[480];
} __attribute__((aligned(16)));
fxsaveResult registerData;
memset(®isterData, 0, sizeof(fxsaveResult));
asm volatile("fxsave %0" : "=m"(registerData));
s_isSupported = registerData.CSRMask & 0x0040;
s_isInited = true;
return s_isSupported;
# endif
}
inline void disableDenormals() {
m_savedCSR = getCSR();
setCSR(m_savedCSR | (isDAZSupported() ? 0x8040 : 0x8000));
}
inline void restoreState() { setCSR(m_savedCSR); }
inline int getCSR() {
int result;
asm volatile("stmxcsr %0" : "=m"(result));
return result;
}
inline void setCSR(int a) {
int temp = a;
asm volatile("ldmxcsr %0" : : "m"(temp));
}
# elif defined(XP_WIN) && defined(_MSC_VER)
inline void disableDenormals() {
// Save the current state, and set mode to flush denormals.
//
// http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly
_controlfp_s(&m_savedCSR, 0, 0);
unsigned unused;
_controlfp_s(&unused, _DN_FLUSH, _MCW_DN);
}
inline void restoreState() {
unsigned unused;
_controlfp_s(&unused, m_savedCSR, _MCW_DN);
}
# elif defined(__arm__) || defined(__aarch64__)
inline void disableDenormals() {
m_savedCSR = getStatusWord();
// Bit 24 is the flush-to-zero mode control bit. Setting it to 1 flushes
// denormals to 0.
setStatusWord(m_savedCSR | (1 << 24));
}
inline void restoreState() { setStatusWord(m_savedCSR); }
inline int getStatusWord() {
int result;
# if defined(__aarch64__)
asm volatile("mrs %x[result], FPCR" : [result] "=r"(result));
# else
asm volatile("vmrs %[result], FPSCR" : [result] "=r"(result));
# endif
return result;
}
inline void setStatusWord(int a) {
# if defined(__aarch64__)
asm volatile("msr FPCR, %x[src]" : : [src] "r"(a));
# else
asm volatile("vmsr FPSCR, %[src]" : : [src] "r"(a));
# endif
}
# endif
};
#else
// FIXME: add implementations for other architectures and compilers
class DenormalDisabler {
public:
DenormalDisabler() {}
// Assume the worst case that other architectures and compilers
// need to flush denormals to zero manually.
static inline float flushDenormalFloatToZero(float f) {
return (fabs(f) < FLT_MIN) ? 0.0f : f;
}
};
#endif
} // namespace WebCore
#endif // DenormalDisabler_h
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